Treatment of oil wells



swimr. nm'mjnmu, cane, a'sllgnor to -"l'he Tens company. New York N. 1., a corporation of Delaware Application July 21, 1938. 4 Serial No. 220.508

-' it claims. (on. 255-1) I drill pipe and thewalls of the hole, so that the j This invention relates to the drilling of wells, and more particularly to the recoveryoi lost :cir-

cula'tlon in wells.

More specifically my invention relatesto the- .l 'method of sealing oil underground crevices and fissures which communicate withthe. well boreby plugging them with a plastic mass comprising a casein putty. I

. In the, drilling times penetrate into an underground cavity'with the result that the drilling mudbeing. circulated through the well is lost into the said cavity, and little or-no drilling mud returns to the surface. Those skille n, the art termthis'condition losing circulation. Y

.Underground cavities are encountered when drilling through almostall types of consolidated iormationa; They occur in various. forms. such as fractures, "fissures. .mrous strata, caverns. and

I o 'otherforms. When such formations are encountered by the drill tools there is'not. only a loss of 'drillingliiu'id, but at the same time the cuttings I a and debris-instead of being'brought to the'surface. by'the drilling mud, accumula e in the hole and may cause serious damage there.

Inthepast-numerous expedients have been;v

employed ineflorts to regain-lostz'circulation.

-"ihesehave included pumping cement in the form] of a slurryj into 'the'ca'vity by circulating the cement down the driiipipe. This method has not sealing even a moderately sized cavity.

.A'nother expedient has involved the use ofv fibrous materials such as straw," hay, wood fiber, and bagassewith a viscous drilling mud, the purpose beingto form a mat oi fibrous material over the opening into the cavity, and in that way pre- 40 vent the loss of drilling mud intothe cavity-from the-well bore! This method however has the disadvantage'that the mats of fibrous material are easily displaced anddo-not effect a permanent repair" I-have discovered a method oi recovering lost circulation which has proved to .be eminently successful. This method involves coating the walls of the well bore, and incidently the opening into the cavity, by means of a thick plastic which comprises an aqueous dispersion of casein and an alkaline earth hydroxide. The method of coating the walls'of the wellbore with the plastic involves placing a quantity of the plastic at the,

bottom of the wellbore and then slowly and interrnittently raising it in the space between the of wells the drilling toolsjsome walls become coated with a layer oi the plastic. The casein-sealing compounds which may be employed in the practice of my invention consists essentially of' alkaline dispersions of casein to.

1 which have been added a sufllcient amount or slated-lime to yield a still pumpable paste. The casein dispersions may with advantage be pre--,-

pared by treating swelled casein with a water solution of an alkaline material such as borax, am- 10 monia, an alkali metal bicarbonate, an alkali metal carbonate, lime, sodium metasilicate, so- I dlum silicate or any equivalent alkaline materials.

I have observed that it may be advantageous to heat both the swelled casein, as well as the solu- 15 tionof alkaline material, inasmuch as the dispersion oi" casein is more rapid and the resulting product is more uniform. Where the casein dispersion is to be stored for anyappreciable length of timeit may be desirable to incorporate therein 20.

small proportions of preservatives such as phenols',-'cresol, camphor, pine oil and the like for I retarding the growth oibacteria or mold.

In order that those skilled in the art may thor oughly understand the preparation of the casein- 25 sealing agent which I employ inthe practice of my invention I give herewith several examples of the preparation of these compositions:

"jroved very satisfactory because the cement f, {slurry spreads out in thin layers and ass. result large quantities of cement maybe required for;

' Example 1 a so Add 61% pounds of casein to 13 gallons of water heated to a temperature of 150 F. and

allow. the casein to soak for at least 15 minutes. Dissolve 11 poundsof granular borax in 2 gallons of water heated to 150 F., then when the casein has soaked for at least 15 minutes mix the thoroughly mixed to yield a stiff but pumpable paste.

casein with the borax solution andstir until the mixture becomes clear.- Then addsufllcient water to bring the volume to gallons. At this point a suitable preservative for the casein such as phenol, camphor 'cresol or the like may be added. when ready to use. the sealing agent the dispersed casein is mixed with about 245 pounds of dry slaked lime and the so-formed mixture is then Example 2 Add 50 pounds of casein I to 15 /2 gallons of water heated to 150 F. and allow to soak for atleast 15' minutes. Dissolve 9 pounds ofpotasslum carbonate in 6 gallons of water heated toa temperature of 150 -F. After the casein has soaked for a sufficient length of time add the solution' of potassium carbonate .to the casein and 'preservatives shown in Example 1 may then be added to the dispersed casein. When it is desired to prepare the casein-sealing compound there is added to the dispersed casein a sufficient amount of fresh slaked lime to yield a stiff but pumpable paste. The amount of lime preferably used is somewhere in the neighborhood of from 175 to 200 pounds.

The amount of alkaline material to be used in preparing the alkaline dispersions of casein is dependent upon the activity of the particular alkaline material selected for the purpose and it is therefore diilicult to state specifically the quantitles to use. However, I have found that in most cases the quantity of alkaline material is preferably in the range of from 10 to 25% by weight of the dry casein.

In preparing the casein dispersions I prefer the use of from 5 to 20% by weight of dispersed casein. However, it is to be understood that more concentrated dispersions may be prepared particularly where it is necessary to transport the casein dispersions appreciable distances.

The amount of lime added to the casein dispersion to obtain the plastic or putty which I use in this invention may vary widely depending upon the concentration of the casein and the type of alkaline dispersing agent used. However. in all cases I contemplate the addition of suflicient slaked lime to the casein dispersion to obtain a thick pumpable paste. Based on the weight of casein in the dispersion this may be of the order of from three to seven times the weight of the casein, assuming the casein dispersion to contain from 5 to 20% by weight of casein.

My invention may with advantage be applied in the following way: v

As soon as circulation is lost a study is made of the well log to determine approximately the location of the break in the casing or in the walls of the hole. When this has been determined the approximate volume of the casein plastic necessary to fill the hole from the bottom to a point past the place where the opening is suspected of being, is calculated. This volume of plastic is then prepared and pumped throfilgh the drill stem to the bottom of the hole, where the plastic is allowed to remain quiescent for a short period of time and, preferably not less than 15 minutes. Thereafter the plastic is alternately raised a short distance and allowed to remain quiescent for at least 15 minutes until the desired section of the well bore has been coated with the casein plastic.

The most effective method of raising the plastic is by displacing it by an equal volume of mud. The actual procedure consists in pumping for a short period of time, preferably that time necessary to raise the plastic 5 to 25 feet or more in the hole and then stopping pumping and allowing the plastic to remain quiescent for a short period of time, preferably not less than 15 minutes. The pumping is then resumed and the material raised another short distance and again allowed to remain quiescent, this process being repeated as many times as are thought necessary to coat the face of the well bore with a thick coating of the plastic.

After the proper section of the hole has been coated with the plastic, the plastic is allowed to remain quiescent and during this time it may be advisable to raise the drill stem and the drill pipe above the portion of the hole undergoing treatment. when the plastic is set circulation of the mud is resumed and the drilling operations can then be proceeded with. I

As a typical example of the practice of my invention I give herewith a description of the method of recovering lost circulation in a well in California. The well had lost circulation and an attempt was made to recover the circulation by pumping into the well a viscous mud prepared from Mojave clay and bentonite but without success. The mud loss was checked as being in the neighborhood of 2.6 barrels per minute. Accordingly 6 drums of a casein dispersion similar to that shown in Example 1 were mixed with eighteen hundred pounds of lime and the soformed plastic was pumped into the drill pipe. This was then followed with 24 barrels of mud. the purpose being to displace the plastic from the drill pipe. The plastic was allowed to remain on the bottom for about 15 minutes and then 8 barrels of mud were used to displace the plastic approximately feet upwardly into the annular space between the drill pipe and the easing, this being done by alternately raising the plastic a short distance and then allowing it to remain quiescent for the proper period of time. Finally the regular drilling mud was thinned with water and circulated down through the drill stem to clean out the drill pipe. When this had been done no appreciable loss in drilling fluid was observed and drilling was resumed without any further diiiflculties with lost circulation.

In another. case circulation was lost while drilling a well in a different California field. An attempt was made to recover lost circulation by employing a thick drilling mud consisting of bentonite and Mojave mud but without success. Thereafter sawdust, cottonseed pulp, wood fiber were pumped down the hole and although circulation was restored for a brief period it was soon lost again. Two more treatments with the same fibrous material followed by 300 barrels of viscous mud were also unsuccessful, it being impossible to restore the circulation. Then both a cement slurry and a mixture of cement and bentonite were used, but both of these materials proved to be unsuccessful. Finally 23 cubic feet of a casein dispersion similar to that shown in Example 1 were mixed with 29 sacks of dry slaked lime to yield approximately 30 cubic feet of casein plastic. This plastic was pumped to the bottom of the well by means of the mud pump and allowed to remain there approximately 15 minutes.

On the basis of my experience I have found it. desirable that the sealing compound be first pumped to the bottom of the hole and then alternately raised a short distance and allowed to remain quiescent until that portion of the hole suspected as containing the opening into the underground cavity is sealed off. If the material is merely pumped to the bottom of the hole and then pumped upwardly in the annular space between the drill pipe and the face of the hole, said sealing action may not be obtained, due apparently to the casein paste not coating the walls of the hole with a sufllciently thick layer of the plastic. l

Although I have described the casein plastics as being mixtures ofalkaline dispersions of casein and slaked lime, I do not intend to limit myself to the use of these materials alone, but contemplate the use therewith o! finely divided solids including clays, bentonite, limestone, iron oxide, litharge and the like in order to alter or modify the physical properties of the casein plastics. I appreciate that in some cases it may be desirable to employ fibrous materials with the plastics, and I therefore contemplate the use with the casein plastics of wood fiber, straw, hay, sugarcane fiber, hair and similar fibrous materials.

Obviously many modifications and variations of the invention as hereinbeiore set forth may be made without departing from the spirit and scope thereof, and only such limitations should be imposed as are indicated 'in the appended claims.

I claim:

1. In the drilling of wells with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall which comprises interrupting the circulation of drilling mud, and coating that portion oi. the well hole containing the opening with a casein plastic by introducing into the well a pumpable casein dispersion containing in excess of by weight of casein on the total weight of the dispersion.

2. In the drilling of wells with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall which comprises stopping the circulation or drilling mud, and coating the walls of the hole containing the opening with a plastic consisting 01' a mixture of a casein dispersion and slaked lime.

3. In the drilling of wells with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall which comprises interrupting the circulation of the drilling mud, pumping a mixture of an aqueous alkaline dispersion of casein and slaked lime to the bottom of the well and then stepwise upwardly along the walls of the well, whereby the opening in the well wall is coated over with the mixture.

4. In the drilling oi wells with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall which comprises interrupting the circulation oi the drilling mud, pumping a mixture of an aqueous alkaline dispersion oi casein and slaked lime to the bottom of the well and then stepwise upwardly along the walls of the hole, whereby the opening in the well wall is coated over with the mixture. and then resuming the circulation oi the drilling mud and drilling of the well.

5. In the drilling of wells with the circulation oi a drilling mud, the method of recovering circulation lost into an opening in the well wall which involves stopping the circulation'oi the drilling mud. pumping a plastic paste comprising an aqueous alkaline dispersion of casein and slaked lime to the bottom of the well, and thenv to the locus of drilling, and the removal of the mud from the well by a second conduit, the method of recovering circulation lost into an opening in the well wall which comprises interrupting the circulation of the drilling mud, pumping a mixture or an aqueous alkaline dispersion of/ casein and slaked lime through the first conduit to the locus of drilling, and then alternately raising the mixture a short distance in the second conduit and allowing it to remain quiescent, until the portion of the well wall containing the opening is coated with the mixture, and then resuming drilling operations.

7. In the drilling of a well with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall, which comprises introducing into the well and into contact with the well wall a pumpable slurry of a casein dispersion containing in excess of 5% by weight of casein on the weight of the slurry, and allowing the slurry to remain in quiescent contact with the well wall for a sufilcient period of time to seal the said opening.

8. In the drilling 01' a well with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall, which comprises introducing into the well and into contact with the well wall a thick pumpable slurry consisting mainly of an aqueous alkaline dispersion of casein and an alkaline earth hydroxide.

9. In the drilling of a well with the circulation of a drilling mud, the method oi recovering circulation lost into an opening in the well wall, which comprises introducing into the well'and into contact with the well wall a thick pumpable slurry consisting mainly 01' an aqueous *alkaline dispersion of casein and hydrated lime. p

10. In the drilling of a' well with the circulation of a drilling mud, the method of recovering circulation lost into an opening in the well wall. which comprises interrupting the circulation of drilling mud, then introducing into the'well and into contact with the well wall a thick pumpable aqueous alkaline earth hydroxide slurry containing a casein plastic, allowing the slurry to remain in contact with the wellwali tor a suiiicient period 01' time to seal the said opening. and then resuming the circulation of the drilling mud and drilling of the well. a

STERLING P. HART. 

